1. Field of the Invention
The present invention relates to resistance welding apparatus and particularly to resistance welding apparatus for joining pipes end to end while laying pipe lines. The invention may prove most advantageous in welding pipes under conditions when the joint region is out of easy reach.
2. Description of the Art
Pipes may be joined by a resistance welding process with the aid of the apparatus having either nondetachable or detachable grip mechanisms. The first type of apparatus offers adequate gripping and alignment of the pipes to be welded but such apparatus have the limitation that either the pipeline has to be pulled through the apparatus or the apparatus has to be pulled over the pipeline with a section of the pipeline being prelaid for the apparatus to move on. Also, a prompt transfer of the apparatus for welding any other joint along the pipeline is a problem with such an apparatus.
The limitations just mentioned are obviated in an apparatus having a detachable grip, since such an apparatus may readily be removed from any section of the pipeline and transferred to any other section or for any other purposes, for example maintenance work. Advantages of such apparatus are most apparent when the pipes to be welded are in close proximity to the ground.
Regardless of the above advantages the apparatus with detachable grip mechanisms have other limitations, namely, the gripping jaws are sectionalized so that their effective surface does not come in contact with the pipe surface along the entire perimeter thereof since the required opening of the grip mechanism and the gripping forces are almost always restricted by hydraulic drive capabilities. Such gripping jaws would not provide gripping of the pipes along the perimeter. As a result, despite the fact that the pipe is deformed, it does not resist the gripping force, which causes slippage of the pipe in the gripping jaws during upsetting.
Known in the art is a resistance welding apparatus having a detachable grip mechanism, wherein the pipe to be welded is gripped along the perimeter thereof by additional or swinging jaws (see technical description and service manual for the welding machine K 581 y I, K 581. 0.00.00.000.TO). This apparatus comprises two pipe gripping means each including a pair of articulated side members and axially aligned for mutual axial movement, each side member being provided with a gripping jaw, welding transformers electrically connected to the gripping jaws and swinging jaws pivoted to the side members for abutting against the pipe surface in their operating position.
In the prior art apparatus the swinging jaw or jaws are put in their operating position manually, that is why an easy access to that side of the apparatus as well as time are required. To put the swinging jaw in position, when laying horizontal pipelines, it is required either to dig a hole of a sufficient depth or to sufficiently raise the pipes. Known in this particular art are means to mechanically operate the swinging jaws, such as an electromechanical drive, a hydraulic drive. These, however, will make the design more complicated in that apart from the drive mechanisms proper, there will be required controls and power equipment. Due to ample dimensions these mechanisms cannot be a complete solution to the problem set forth hereinbefore as regards laying horizontal pipelines.